THE ARKANSAS COAL MEASURES. 193 



sular India and Afghanistan. Brazil probably belongs to this type, 

 but is to a certain extent transitional. 



The Itaituba fmma. — A comparison of the Upper Carbonifer- 

 ous fauna of Itaituba, Brazil, as described in part by Professor O. 

 A. Derby,' shows that of 27 species of Brachiopoda, 12 are iden- 

 tical with American forms, although most of these are cosmo- 

 politan. The genus Strophalosia is common in these beds, and as 

 Professor Derby ^ says, the species shows affinity with the Permian. 

 Many of the new species described by Professor Derby are closely 

 related to the European forms. Waagens says that the beds of 

 Itaituba are of the same age as the Middle Productus limestone of 

 India, that is of the Permo-Carboniferous transition beds. The 

 Brazilian Strophalosia is closely related to Australian species, indi- 

 cating a closer connection with the Australian or southern Car- 

 boniferous region than with the Pacific province. Hence we infer 

 that the Brazilian deposits may after all belong to the Upper Coal 

 Measures, and that the difference between them and the northern 

 Upper Coal Measures may be geographic instead of geologic. 



CLASSIFICATION AND AGE OF THE ARKANSAS COAL MEASURES. 



Provisiofial classification. — For the sake of convenience, the 

 Coal Measures of Arkansas have been provisionally classified by 

 the Survey as Upper or Productive, and Lower or Barren Coal 

 Measures. This division is not based on any paleontologic or 

 stratigraphic break, but merely on the occurrence or non-occur- 

 rence of coal. 



The divisions that are recognized in Pennsylvania could not 

 be recognized in Arkansas, but the strata of the two regions are 

 correlated as far as possible with the scanty data now at hand. 



The Lozver Coal Measures. — Of the age of the Lower Coal 

 Measures we have only stratigraphic evidence, their position 

 above the limestone of the Lower Carboniferous, and below the 

 coal-bearing beds of the Lower Coal Measures being unmistakable. 



'Bulletin Cornell University, Vol. I., No. 2. 



^Op. cit., p. 60. 



3 Salt Range Fossils, "Geological Results," p. 207. 



